Direct current to alternating converters exist in which the output is a square wave, for example, the vibratory driven switch. The solid state, transistorized or controlled rectifier direct current to alternating current wave is more recent. The d.c. to a.c. converter capable of supplying a sine wave output enjoys considerable market potential; for example, standby systems (on failure) can replace the commercial sine wave voltage source, with the converter deriving its energy from a battery.
A typical single phase constant circuit comprises a constant voltage transformer with a source of rectangular wave input. The constant potential transformer is that of U.S. Pat. No. 2,143,745 issued Jan. 10, 1939 to J.G. Sola. This transformer is designed and intended to provide a voltage regulated alternating current sine wave output from a fluctuating alternating current sine wave input.
The typical prior art three phase inverter power circuit comprises simply three constant voltage transformers with three rectangular wave inputs -- three single phase circuits. These prior art three phase power circuits, in addition to having redundant components that are bulky and expensive, are not satisfactory for delta type of loads. Also output voltage regulation under load unbalances has been less than desirable. The oscillator, that provides the input frequency, is a high accuracy oscillator that is stable under all operating conditions. However, at the transformer outputs there does occur variations in phase from one output to another when an unbalanced load is applied.